There are many situations in industrial processes in which it is required that a thin film of a particular liquid substance be coated onto a receiving surface. For example, in a typical printing press, a series of rollers is employed to transfer specified amounts of printing ink or other liquid coatings to the surface of a printed web or an adjacent roller. It has been found that the distribution of ink and other fluid coatings is facilitated by providing for the simultaneous oscillation or vibration of these rollers along their rotational axes during roller rotation.
Some oscillating roller assemblies undergo the requisite oscillation by way of an oscillation means that is maintained externally from the roller to which the oscillating motion is imparted. Other oscillating roller assemblies employ an oscillation means that is maintained within the roller itself. The latter configuration typically employs some means by which a portion of the rotational force initially delivered to the roller is subsequently translated into an oscillating force by a mechanism internally disposed within the roller.
With respect to oscillating roller assemblies having an internally disposed oscillation means, it has been determined that the distribution of printing fluids or coatings by such rollers can be further enhanced where the velocity of oscillation is not solely a function of the rotational velocity of the roller, but is rather a function of the rotational velocity of the roller in conjunction with a means for accurately and independently reducing and maintaining a constant velocity for that portion of the rotational force which is subsequently translated into an oscillating movement.
In the past, various mechanisms have been developed in the printing industry to achieve the simultaneous oscillation of a roller during rotation. For example, U.S. Pat. No. 4,777,877 discloses an apparatus and method providing for the oscillation of ink form rollers in a printing press wherein the oscillating motion is imparted to the rollers by an outboard gear system that is maintained externally to the rollers. Similarly, U.S. Pat. No. 4,753,167 discloses a vibrator roller assembly wherein the vibrational or oscillating movement is imparted to the roller by way of a shaft driven by an externally maintained drive mechanism.
Although externally positioned oscillation mechanisms effectively impart an oscillating movement to a roller at a velocity which can be manipulated independently from the rotational velocity of the roller, a major shortcoming presented by such outboard oscillation mechanisms is that additional space is needed in order to accommodate the mechanism within or around the frame which supports the rollers. These spatial considerations become especially problematic when modifying an existing printing press assembly to receive an oscillating roller or when performing an in-line integration of an existing printing press unit with a coating mechanism containing rollers having an oscillation capability.
In response to the foregoing problem, oscillating rollers having inboard or internally contained means for oscillation were developed. For example, U.S. Pat. No. 4,337,699 discloses an oscillating roller 1 having an oscillation means contained within the roller jacket 2. The oscillating movement is achieved by two bushings and a ball bearing disposed within the roller jacket. A first bushing 15 revolves as a cage about a central shaft 4 and contains an elliptical groove 19 while the second bushing 13 is fixed within the roller jacket 2 and contains a circular groove 20. A ball bearing 21 travels in a keyway or channel created between grooves 19 and 20, thereby translating a portion of the rotational force imparted to the roller 1 into an oscillating force. The velocity of the oscillation is essentially a function of the rotational speed of the roller, although some reduction in speed does occur via friction between the ball bearing 21 and the channel created by grooves 19 and 20. No definitive means for accurately modifying or reducing the velocity of oscillation is provided.
Similarly, U.S. Pat. No. 4,869,167 discloses a variable-speed oscillating roller having an oscillation means contained within the roller. The oscillation means translates a portion of the rotational force imparted to the roller into an oscillating movement by way of a key 22 traveling in a groove or screw slot 24 present on the outer surface of a sleeve 18. The sleeve 18 is concentrically mounted about a shaft 14 which initially imparts the rotational force to the roller. An adjustment means 38 is provided to control the amount of frictional engagement which occurs between the sleeve 18 and the roller 12. By adjusting the degree of frictional engagement between the sleeve 18 and the roller 12, the rotational velocity of the sleeve 18 can be reduced relative to the rotational velocity of the roller 12. Consequently, the velocity of the oscillation is a function of both the rotational speed of the roller 12 and the degree of frictional engagement between the roller 12 and the sleeve 18.
A major shortcoming in both of the oscillating rollers previously described is that either the oscillation velocity is essentially only a direct function of the rotational velocity of the roller or it is partially dependent upon frictional mechanisms which are very difficult to establish and maintain. For example, some surface areas may undergo wear more readily than others, thereby resulting in a non-uniform oscillation velocity due to irregularities in the amount of friction present over the period of oscillation. Variations in oscillation velocity impair the uniform distribution of any liquid substance in which the roller is involved in transferring. In a coating apparatus employed in a printing press, a non-uniform distribution of the coating liquid applied to a web or an adjacent roller results in undesirable, coater-imposed patterns such as orange peel, striation and volcanoing.
An additional shortcoming of oscillating rollers having similar groove configurations to those rollers previously mentioned is that the oscillating motion becomes irregular at the edges of the oscillation cycle as the roller terminates its axial movement in one direction and proceeds to oscillate back in the opposite direction. This phenomenon also contributes to the undesirable coater-imposed aberrations previously mentioned.
Consequently, it is an object of the present invention to provide an improved coating system having an oscillating roller for use in a printing press to deliver a controlled, evenly distributed coating or layer of a fluid substance to a printed web or other material without undesirable, roller-imposed coating aberrations such as orange peel, volcanoing and striations.
It is another object of the present invention to provide a new oscillating roller assembly for a coating mechanism whereby the coating mechanism delivers a controlled, evenly distributed fluid coating to a printed web or other material without undesirable roller-imposed coating aberrations such as orange peel, volcanoing in striations.
It is yet another object of the present invention to provide a new oscillating roller assembly which delivers a controlled, evenly distributed coating or layer of a fluid substance to the surface of a printed web or adjacent roller.
It is also a further object of the present invention to provide a new oscillating-metering roller assembly for a coating mechanism whereby the oscillating-metering roller performs a metering function in addition to delivering a controlled, evenly distributed coating or layer of a fluid substance to the surface of a printed web or adjacent roller without undesirable, roller-imposed coating aberrations such as orange peel, volcanoing and striations.
It is finally an object of the present invention to provide a new oscillating roller assembly for a coating mechanism having an internally disposed oscillation means which imparts a smooth and uniform oscillating motion to the roller at a constant velocity, the oscillation velocity being a function of the rotational velocity of the roller in conjunction with a means for accurately and independently modifying and maintaining the velocity of the portion of the rotational force that is to be subsequently translated into an oscillating force.